Illumination warm-up control in a document scanner

Abstract

A method for determining when overall lamp intensity is stable for a lamp in a document scanner. The intensity of a relatively small portion of the lamp is controlled as part of a closed loop intensity control system. During a warm-up transient period, the intensity of the small portion of the lamp is monitored and power to the lamp is monitored. A changing power to the lamp indicates that the overall lamp intensity has not stabilized. Scanning is initiated when the intensity of the monitored portion of the lamp is within a predetermined control range and the power to the lamp has stabilized for a predetermined time period. The predetermined time period can be a default value or can be determined by a user.

What is claimed is: 
     
       1. A method for determining when a scan in a document scanning device is initiated after initial application of power to a lamp, the method comprising the following steps: a. applying electrical power to the lamp;   b. monitoring intensity of a particular portion of the lamp;   c. controlling power to the lamp to maintain the intensity of the particular portion of the lamp within a predetermined intensity range;   d. monitoring power to the lamp; and   e. initiating the scan by the scanning device if the intensity of the particular portion of the lamp is within the predetermined intensity range and if the power to the lamp is substantially constant for a predetermined amount of time.   
     
     
       2. The method of claim 1 wherein the lamp is an electric-discharge lamp. 
     
     
       3. A method for determining when a scan in a document scanning device is initiated after initial application of power to a lamp, the method comprising the following steps: a. receiving an input from a user, the input indicative of an amount of time;   b. applying electrical power to the lamp;   c. monitoring intensity of a particular portion of the lamp;   d. controlling power to the lamp to maintain the intensity of the particular portion of the lamp within a predetermined intensity range;   e. monitoring power to the lamp; and   f. initiating the scan by the scanning device if the intensity of the particular portion of the lamp is within the predetermined intensity range and if the power to the lamp is substantially constant for the amount of time specified by the input from the user.   
     
     
       4. The method of claim 3 wherein the lamp is an electric-discharge lamp.